1. Field of the Invention
The present invention is related to an image processing apparatus, an image processing method, and an image processing program for administering image processes onto fluorescent images that represent blood vessels, obtained by an endoscope.
2. Description of the Related Art
Recently, NBI (Narrow Band Imaging) apparatuses which have built in combinations of narrow bandpass filters and which are employed to perform spectral imaging based on spectral reflectance of digestive organs (gastric mucosa and the like), are gaining attention as imaging apparatuses such as electronic endoscopes that employ solid state imaging elements. These apparatuses are equipped with narrow (wavelength) bandpass filters instead of rotating frame sequential R (red), G (green), and B (blue) filters. Illuminating light beams are sequentially output via these narrow bandpass filters, and spectral images are formed by administering processes similar to those administered onto RGB signals while changing the weighting of three signals obtained by each illuminating light beam. Fine structures, which had heretofore been unobtainable, are capable of being extracted within digestive organs such as stomachs and large intestines from these spectral images.
On the other hand, Japanese Unexamined Patent Publication No. 2003-093336 discloses forming spectral images by administering calculation processes on image signals obtained by imaging using white light using a simultaneous method in which a fine mosaic color filter is provided on a solid state imaging element, instead of the aforementioned frame sequential method that employs the narrow bandpass filters. In this method, relationships among numerical data that represent color sensitivity properties of R, G, and B, and numerical data that represent spectral properties of specific narrow wavelength bands are obtained as matrix data (set of coefficients). Spectral image signals, which are estimations of spectral images obtained via narrow bandpass filters, are obtained by calculations among the matrix data and R, G, and B signals. In the case that the spectral images are obtained by calculations in this manner, it is not necessary to prepare a plurality of filters that correspond to each desired wavelength range. In addition, replacement of filters is obviated. Therefore, the size of an apparatus that employs this method can be kept small, and costs can be suppressed.
Meanwhile, a method in which blood vessels, cancer cells and the like are labeled with fluorescent reagents and fluorescent images thereof are observed is employed in the field of living tissue observation. Applying the aforementioned techniques regarding spectral images to obtain the fluorescent images is being considered. Fluorescent images are employed to understand the accurate positions of blood vessels by intravenously injecting a fluorescent reagent, such as ICG (Indo Cyanine Green). Here, by obtaining light in the near infrared region of 700 nm to 1300 nm, at which attenuation due to living tissue is small, as the fluorescent images, the positions of blood vessels can be specified even at depths of approximately 2 mm from a surface layer.
In addition, an image processing method is disclosed, in which blur within images is estimated based on prognostic simulations and point spreads of actually obtained images, then a reconstructing process is administered, to obtain sharper images of blood vessels (refer to U.S. Pat. No. 5,879,284, for example).
Here, applying the blood vessel emphasizing process disclosed in U.S. Pat. No. 5,879,284 to fluorescent imagesmaybe considered, in order to improve the sharpness of blood vessel images within fluorescent images. However, the degree of blur of blood vessel images differs within fluorescent images according to the depth positions of the blood vessels. Therefore, there is a problem that image quality does not improve in cases that image quality improving processes are administered employing a uniform point spread. Meanwhile, the depth positions of blood vessels cannot be discriminated within fluorescent images, and as a result, there is a problem that it is difficult to improve the image quality of fluorescent images.